1. Field of the Invention
The present invention relates to a network formed with a plurality of private branch exchanges (hereinafter referred to as xe2x80x9cPBXxe2x80x9d), and more particularly to an improvement when an extension group is formed over more than one PBX.
2. Description of the Related Art
FIG. 1 is a block diagram showing a configuration of a private branch exchange system using a prior art PBX. In FIG. 1, PBX 3 supporting a plurality of extension telephones 4 constituting extension group 5 is provided for each floor level of a building or for each office, for example. Each extension telephone 4 is assigned a unique extension number. CPU 10 is provided inside PBX 3 for performing switching processing, and accesses database 8 which stores extension numbers of extension telephones 4. Trunk circuit 2 is a circuit for relaying external telephone network 1 to PBX 3. External telephone network 1 is a public line constructed by a communication provider, and includes, for example, local call, long distance call, international telephone, and portable telephone networks.
FIG. 2 is a block diagram showing a configuration of a prior art apparatus when a plurality of PBXs are connected through a control device. Extension group 5a managed by first PBX 3a is connected to extension group 5b managed by second PBX 3b through communication line 12 and call distribution control device 13. Call distribution control device 13 transforms an overflow call in extension group 5a to group 5b. The overflow call refers to a state where a call from external telephone network 1 can not be quickly answered since all extension telephones 4a belonging to extension group 5a are busy.
However, according to the apparatus in FIG. 1, since extension group 5 need be closed for one PBX, there is a problem of a limited range of the expansion of telephones 4 and extension groups 5. As a result, existing PBXs can not provide flexible support either for an increase in the number of connected extension telephones 4 by a user of the extension, or for a change in extension groups 5 associated with organizational modifications.
Additionally, according to the apparatus in FIG. 2, since the transfer of the overflow call in extension group 5a to group 5b by overflow call control device 13 is merely secondary processing, a problem exists in that extension telephone 4b to be connected is not instantly determined, resulting in a longer time to keep a calling customer waiting. Furthermore, no close connections among CPU 10a, CPU 10b and device 13 cause a problem of poor maintainability such as difficulties of synchronous database upgrade.
The present invention solves the aforementioned problems, and it is an object of thereof to provide a private branch exchange network system which facilitates the expansion of extension telephones and extension groups and which can quickly transfer an overflow call from extension telephones supported by one PBX to an extension telephone supported by another PBX.
The private branch exchange network(PBX network) system connected to telephone network 1 of the present invention for solving the aforementioned problems is formed such that a plurality of PBXs 3a and 3b are connected to each other with communication line 6 and accommodating a plurality of extension telephones 4, respectively through private lines. Each of the PBXs comprises first means for detecting an incoming call arriving through telephone network 1 to queue the incoming call in reception sequence queue 7 common in the overall PBX network, second means for scanning a distribution sequence queue 9 supporting extension group 5 including extension telephones accommodated by each of the PBXs to select an extension telephone so as to equalize load, and third means for connecting the incoming call to the selected extension telephone when the extension telephone selected by the second means is accommodated by one PBX in which the incoming call is detected, and when the extension telephone selected by the second means is accommodated by another PBX, for transferring the incoming call to the other PBX through the communication line.
With the configuration as described above, the first means queues an incoming call arriving through telephone network 1 in reception sequence queue 7 common in the overall PBX network to determine the reception sequence of the incoming call. The second means scans distribution sequence queue 9 common in the overall PBX network to select an extension telephone so as to equalize load. The third means connects the incoming call to an extension telephone determined from reception sequence queue 7 and distribution sequence queue 9. Specifically, when the extension telephone is accommodated by one PBX in which the incoming call is detected, the incoming call is connected to the extension telephone, and when the extension telephone is accommodated by another PBX, the incoming call is transferred to the other PBX through the communication line.
The private branch exchange network system of the present invention is configured such that each of the PBXs transfers, when faulty, an incoming call directed to that PBX from telephone network 1 to another PBX through communication path 11 for bypassing and the communication line. With such a configuration, even a faulty PBX may be replaced with another PBX serving as a backup which is connected through the PBX network, thereby enhancing reliability.
Additionally, in the private branch exchange network system of the present invention, each of the PBX is configured such that, when a PBX is faulty, extension telephones accommodated by the faulty PBX are removed from extension telephones to be assigned in the distribution sequence queue with the second means. With such a configuration, even when one PBX is faulty, determination is made in the distribution sequence queue with an extension telephone accommodated by another PBX connected through the PBX network, thereby enhancing reliability as compared with a concentrated type which accommodates a number of extension telephones for one PBX.
As described above, according to the private branch exchange network system of the present invention, an incoming call arriving through the telephone line is queued in the reception sequence queue common in the overall PBX network, and the distribution sequence queue common in the overall PBX network is scanned to select an extension telephone so as to equalize load, and then the incoming call is distributed and connected to the extension telephone. Since the distribution and connection are performed for extension telephones accommodated by a plurality of PBXs connected each other with the communication line, it is possible to connect a new PBX to an existing PBX through a communication line to operate easily as an integrated private branch exchange network system, providing the effect that the system configuration is readily modified and expanded. As in an order reception center of mail order, for example, the system generates no difference in telephone services between a minimum configuration of one PBX and an expanded version of n PBXs, so that it is optimal with no impact on customers. In companies which introduce the system, even distributed or integrated departments due to organizational modifications may be readily supported by integrating PBXs set in the respective departments through communication lines, and an additional effect occurs in that a capital investment can be reduced.
Additionally, even when respective customers are notified of different telephone numbers for allowing the customers to call their nearest PBXS, uniform services can be provided since responding extension telephones are logically selected from the overall system. Since a dedicated communication line of flat rate can be used for the communication line which connects PBXs, telephone rates can be reduced, and the effect is greater especially in collect calls.